• Software Defined Radio Block Diagram

Rapid Prototyping Interface for Software Defined Radio Experimentation by Michael Joseph Leferman A Thesis Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE in partial ful llment of the requirements for the Degree of Master of Science in Electrical and Computer Engineering by February 2010 APPROVED: Dr. Alexander Wyglinski, Major. Before joining KFUPM, he worked as a Project Engineer in Wipro Technologies, a leading MNC in Bangalore, India (2009-2010), where he was part of a Testing.

Luis Chaparro, in, 2015 0.2.2 Software-Defined Radio and Cognitive RadioSoftware-defined and cognitive radio are important emerging technologies in wireless communications 44. In software-defined radio (SDR), some of the radio functions typically implemented in hardware are converted into software 65. By providing smart processing to SDRs, cognitive radio (CR) will provide the flexibility needed to more efficiently use the radio frequency spectrum and to make available new services to users. In the United States the Federal Communication Commission (FCC), and likewise in other parts of the world the corresponding agencies, allocates the bands for different users of the radio spectrum (commercial radio and TV, amateur radio, police, etc.). Although most bands have been allocated, implying a scarcity of spectrum for new users, it has been found that locally at certain times of the day the allocated spectrum is not being fully utilized.

Cognitive radio takes advantage of this. Conventional radio systems are composed mostly of hardware, and as such cannot be easily reconfigured. The basic premise in SDR as a wireless communication system is its ability to reconfigure by changing the software used to implement functions typically done by hardware in a conventional radio. In an SDR transmitter, software is used to implement different types of modulation procedures, while A/D and D/A coverters are used to change from one type of signal into another. Antennas, audio amplifiers, and conventional radio hardware are used to process analog signals. Typically, an SDR receiver uses an A/D converter to change the analog signals from the antenna into digital signals that are processed using software on a general purpose processor.

See Figure 0.2. Schematics of a voice SDR mobile two-way radio. Transmitter: the voice signal is inputted by means of a microphone, amplified by an audio amplifier, converted into a digital signal by an analog-to-digital converter (ADC) and then modulated using software, before being converted into analog by a digital-to-analog converter (DAC), amplified and sent as a radio frequency signal via an antenna.

Receiver: the signal received by the antenna is processed by a superheterodyne front-end, converted into a digital signal by an ADC before being demodulated and converted into an analog signal by a DAC, amplified and fed to a speaker. The modulator and demodulator blocks indicate software processing.Given the need for more efficient use of the radio spectrum, cognitive radio (CR) uses SDR technology while attempting to dynamically manage the radio spectrum. A cognitive radio monitors locally the radio spectrum to determine regions that are not occupied by their assigned users and transmits in those bands. If the primary user of a frequency band recommences transmission, the CR either moves to another frequency band, or stays in the same band but decreases its transmission power level or modulation scheme to avoid interference with the assigned user. Moreover, a CR will search for network services that it can offer to its users.

Thus SDR and CR are bound to change the way we communicate and use network services. David Kleidermacher, Mike Kleidermacher, in, 2012 6.4.1 Red-Black SeparationSoftware-defined radios (SDRs) that process classified information are typically architected with a standard red-black separation in which a red side is responsible for sensitive information processing and cryptographic functions, and the black-side processor is responsible for communication stacks and drivers. The red and black sides are hosted on separate hardware components. In fact, the red side is usually composed of both a general-purpose processor and a separate cryptographic processor. Chaparro, Aydin Akan, in, 2019 0.2.2 Software-Defined Radio and Cognitive RadioSoftware-defined and cognitive radio are important emerging technologies in wireless communications 48.

In a software-defined radio (SDR), some of the radio functions typically implemented in hardware are converted into software 69. By providing smart processing to SDRs, cognitive radio (CR) will provide the flexibility needed to more efficiently use the radio frequency spectrum and to make available new services to users. In the United States the Federal Communication Commission (FCC), and likewise in other parts of the world the corresponding agencies, allocates the bands for different users of the radio spectrum (commercial radio and TV, amateur radio, police, etc.). Although most bands have been allocated, implying a scarcity of spectrum for new users, it has been found that locally at certain times of the day the allocated spectrum is not being fully utilized.

Cognitive radio takes advantage of this. Conventional radio systems are composed mostly of hardware, and as such cannot easily be re-configured. The basic premise in SDR as a wireless communication system is its ability to reconfigure by changing the software used to implement functions typically done by hardware in a conventional radio. In an SDR transmitter, software is used to implement different types of modulation procedures, while analog-to-digital converters (ADCs) and digital-to-analog converter (DACs) are used to change from one type of signal into another.

Antennas, audio amplifiers and conventional radio hardware are used to process analog signals. Typically, an SDR receiver uses an ADC to change the analog signals from the antenna into digital signals that are processed using software on a general-purpose processor.

Software Defined Radio Block Diagram

Schematics of a voice SDR mobile two-way radio. Transmitter: the voice signal is inputted by means of a microphone, amplified by an audio amplifier, converted into a digital signal by an analog-to-digital converter (ADC) and then modulated using software, before being converted into analog by a digital-to-analog converter (DAC), amplified and sent as a radio frequency signal via an antenna. Receiver: the signal received by the antenna is processed by a superheterodyne front-end, converted into a digital signal by an ADC before being demodulated and converted into an analog signal by a DAC, amplified and fed to a speaker. The modulator and demodulator blocks indicate software processing.Given the need for more efficient use of the radio spectrum, cognitive radio (CR) uses SDR technology while attempting to dynamically manage the radio spectrum. A cognitive radio monitors locally the radio spectrum to determine regions that are not occupied by their assigned users and transmits in those bands. If the primary user of a frequency band recommences transmission, the CR either moves to another frequency band, or stays in the same band but decreases its transmission power level or modulation scheme to avoid interference with the assigned user. Moreover, a CR will search for network services that it can offer to its users.

Thus SDR and CR are bound to change the way we communicate and use network services. Danijela Cabric. Ronan Farrell, in, 2010 19.4.1 IntroductionSoftware-defined radio (SDR) technologies are rapidly maturing, and it is becoming feasible to consider their use in commercial systems. Much of the emphasis in software and cognitive radio research has focused on the challenges faced by the mobile user; however, the fixed base station infrastructure can benefit greatly from the application of SDR/CR techniques. Many immediate cost benefits drive the increased use of SDR techniques in base stations, for example, improved time to market in the face of evolving standards or the benefits of a single platform for multiple standards. There are also operator benefits. Mobile phones and other client devices are consumer devices with minimal cost implementations.

Base stations that follow a software radio paradigm can support multiple devices within a single wireless access network, allowing network operators to offer a wider range of services. Again from the network perspective, the move toward femtocells to offer increased broadband services to existing mobile clients requires femtocells to detect, configure, and self-manage in an independent distributed fashion. This will drive further deployment of software-defined and cognitive radio technologies into the network access infrastructure.Wireless base stations offer certain advantages that encourage deployment of SDR technologies: They are typically wire powered and expensive. This means that they can more reasonably afford the additional processing power and costs required by SDR systems. On the other hand, base stations present a different set of challenges to the SDR community. To ease the performance requirements of a mobile device, base stations have a significantly higher performance requirement, in terms of sensitivity to weak received signals, transmit power, linearity, and bandwidth. Recently there has been a convergence of some aspects of base stations and clients: femtocells base stations mean that power and computational resources are more limited; wideband communication schemes mean that clients must now match the base stations in spectral bandwidth.

However, the linked issues of linearity and sensitivity remain. A decrease in linearity or sensitivity would have unacceptable impacts on overall network performance or mobile client power consumption.In 2004, the National University of Ireland Maynooth joined a research collaboration, the Centre for Telecommunications Value Chain Research. This was a consortium of five universities and Bell Labs, now part of Alcatel-Lucent.

As part of this collaboration we began an investigation into software-defined radio platforms for use in base stations. The objective of this program was to investigate the challenges in developing a practical system from a base station perspective and implement a fully integrated software and hardware SDR/CR platform in partnership with the IRiS software radio framework of Trinity College Dublin 670. In the following subsections, the key issues faced in designing the Maynooth adaptable radio system (MARS) are discussed. Platform ObjectivesWhen designing any radio platform, a number of design choices need to be made to meet the objectives and constraints of the radio, for example, operating frequency, resilience to interference, signal processing requirements, and available technologies. For a reconfigurable radio platform these issues become more complex.

When a standard is developed the performance objectives and constraints are balanced in such a way as to achieve the optimal feasible performance. In a reconfigurable radio platform that is targeted at supporting multiple standards, typically the radio design must take into account the worst-case constraint for each standard and cannot rely on any leniency an individual standard may have provided. As a result, with some notable exceptions 671, 672, most experimental cognitive radio platforms do not attempt to match standards but to provide frequency and waveform flexibility. The Maynooth adaptable radio system platform.

▪Future base stations. In 2005, when this project started, most base stations supported a frequency band no greater than 5 MHz. However, there is strong interest in a base station that could support distinct and separated bands of frequencies, enabling base station sharing between operators or where operators may own different bands of frequency. This drove a specification that full-band support should be explored, 70 MHz over an approximate 700 MHz range. Since the start of the project, wideband schemes such as wCDMA and WiMAX have become increasingly popular and bandwidths of at least 25 MHz need to be supported. ▪General-purpose computer connected. Much of the work on software and defined and cognitive radio is undertaken by researchers more familiar with general-purpose processors than FPGA or DPS devices.

The vision of this project is to provide an interface with a general-purpose computer in which modulated baseband data are passed between the computer and the radio platform. This can be easily identified as a performance bottleneck, as one must choose a standardized interface.

At the start of this project, high-performance interfaces were limited and, on the assumption that it must be widely supported and not require alteration of the computer, the USB2 standard was selected. This choice has had a significant impact on system performance, which is detailed later. ▪Communication modes between 1700 and 2450 MHz. This range of frequencies is comparatively narrow but is the most congested frequency range for personal communications. As a project specification we identified the following communication modes that are to be supported: GSM1800, PCS1900, IEEE 802.11b/g, UMTS (TDD and FDD).In addition, the Irish communications and spectrum regulator (ComREG) licensed to our university two 25 MHz bands of spectrum at 2.1 and 2.35 GHz. A software defined radio is a radio in which the properties of carrier frequency, signal bandwidth, modulation, and network access are defined by software. Modern SDR also implements any necessary cryptography, forward error correction coding, and source coding of voice, video, or data in software as well.

As shown in the timeline of Figure 1.2, the roots of SDR design go back to 1987, when Air Force Rome Labs (AFRL) funded the development of a programmable modem as an evolutionary step beyond the architecture of the integrated communications, navigation, and identification architecture (ICNIA). ICNIA was a federated design of multiple radios—that is, a collection of several single-purpose radios used as one piece of equipment. SDR timeline. Images of ICNIA, SPEAKeasy-I, SPEAKeasy-II, and DMR on their contract award timelines and corresponding demonstrations. These radios are the evolutionary steps that led to today's SDRs.Today's SDR, in contrast, is a general-purpose device in which the same radio tuner and processors are used to implement many waveforms at many frequencies. The advantage of this approach is that the equipment is more versatile and cost effective.

Additionally, it can be upgraded with new software for new waveforms and new applications after sale, delivery, and installation. Following the programmable modem, AFRL and DARPA joined forces to fund the SPEAKeasy-I and SPEAKeasy-II programs.SPEAKeasy-I was a six-foot-tall rack of equipment (not easily portable), but it did demonstrate that a completely software programmable radio could be built, and included a software programmable crytography chip called Cypress, developed by Motorola Government Electronics Group (subsequently purchased by General Dynamics).

SPEAKeasy-II was a complete radio, packaged in a practical radio size (the size of a stack of two pizza boxes), and was the first SDR to include programmable voice coder (vocoder), and sufficient analog and digital signal-processing resources to handle many different kinds of waveforms. It was subsequently tested in field conditions at Ft. Irwin, California, where its ability to handle many waveforms underlined its extreme utility, and its construction from standardized commercial off-the-shelf (COTS) components was a very important asset in defense equipment. SPEAKeasy-II was followed by the US Navy's Digital Modular Radio (DMR), becoming a four-channel full duplex SDR, with many waveforms and many modes, able to be remotely controlled over an Ethernet interface using Simple Network Management Protocol (SNMP).These SPEAKeasy-II and DMR products evolved, not only to define these radio waveform features in software, but also to develop an appropriate software architecture to enable porting the software to an arbitrary hardware platform and thus to achieve hardware independence of the waveform software specification.

This critical step allows the hardware to evolve its architecture independently from the software, and thus frees the hardware to continue to evolve and improve after delivery of the initial product. The basic hardware architecture of a modern SDR ( Figure 1.3) provides sufficient resources to define the carrier frequency, bandwidth, modulation, any necessary cryptography, and source coding in software. The hardware resources may include mixtures of GPPs, DSPs, field-programmable gate arrays (FPGAs), and other computational resources, sufficient to include a wide range of modulation types (see Section 1.2.1). In the basic software architecture of a modern SDR ( Figure 1.4), the application programming interfaces (APIs) are defined for the major interfaces to ensure software portability across many very different hardware platform implementations, as well as to ensure that the basic software supports a wide diversity of waveform applications without having to be rewritten for each waveform or application. The software has the ability to allocate computational resources to specific waveforms (see Section 1.2.3).

It is normal for an SDR to support many waveforms interfaced to many networks, and thus to have a library of waveforms and protocols. Basic hardware architecture of an SDR modem. The hardware provides sufficient resources to define the carrier frequency, bandwidth, modulation, any necessary cryptography, and source coding in software. The hardware resources may include mixtures of GPPs, DSPs, FPGAs, and other computational resources, sufficient to include a wide range of modulation types.

Note: A/D = analog to digital; AGC = automatic gain control; D/A = digital to analog; DSP = digital signal processor; FPGA = field-programmable gate array; GPP = general-purpose processor; IF = intermediate frequency; LNA = low-noise amplifier; RF = radio frequency. Basic software architecture of a modern SDR. Standardized APIs are defined for the major interfaces to ensure software portability across many very different hardware platform implementations. The software has the ability to allocate computational resources to specific waveforms. It is normal for an SDR to support many waveforms to interface to many networks, and thus to have a library of waveforms and protocols. Max Robert, Bruce A. Fette, in, 2009 3.8 SummaryAlthough a software-defined radio is not a necessary building block of a cognitive radio, the use of SDR in CR can provide significant capabilities to the final system.

An SDR implementation is a system decision, in which the selection of both the underlying hardware composition and the software architecture are critical design aspects.The selection of hardware composition for an SDR implementation requires an evaluation of a variety of aspects, from the hardware's ability to support the required signals to other performance aspects, such as power consumption and silicon area. Traditional approaches can be used to estimate the needs at the RF and data acquisition levels.

At the processing stage, it is possible to create an estimate of a processing platform's ability to be able to support a particular set of signal-processing functions. With such an analysis, it is possible to establish the appropriate mix of GPPs, DSPs, FPGAs, and CCMs for a particular set of signal-processing needs.In order to mimic the nature of a hardware-based radio, with components such as mixers and amplifiers, component-based programming is a natural way to consider software for SDR. In CBP, components are defined in terms of their interfaces and functionality.

This definition provides the developer with significant freedom on the specific structure of that particular component.Even though a developer may choose to use CBP for the design of an SDR system, a substantial infrastructure is still needed to support SDR implementations. This infrastructure must provide basic services, such as the creation and destruction of waveforms, as well as general system integration and maintenance. The goal of a software architecture is to provide this underlying infrastructure.

The Software Communications Architecture is one such architecture. The SCA provides the means to create and destroy waveforms, manage hardware and distributed file systems, and manage the configuration of specific components.Finally, beyond programming methodologies and architectures are the actual languages that one can use for development of waveforms and the specific patterns that are chosen for the developed software. These various languages have different strengths and weaknesses.

C and Java are the dominant languages in SDR today. Python, a scripting language, has become increasingly popular in SDR applications, and is likely to be an integral part of future SDR development.Much like the language selection, a design pattern for a particular component can have a dramatic effect on the capabilities of the final product. Design patterns that focus on flexibility can be more readily applied to cognitive designs, from the most basic node development all the way up to full cognitive networks.

SUO-SAS (Small Unit Operations—Situation-Awareness System)Developed by DARPA to establish the operational benefits of an integrated suite of advanced communication, navigation, and situation awareness technologies. It serves as a mobile communications system for small squads of soldiers operating in restrictive terrain. SUO-SAS provides a navigation function utilizing RF ranging techniques and other sensors to provide very high accuracy 22.DMR (Digital Modular Radio)A full SDR capable of interoperability with tactical systems such as HF, DAMA, HaveQuick, and SINCGARS, as well as data link coverage for Link-4A and Link 11. These systems are programmable and include software-defined cryptographic functions. The US Navy is committed to migrating DMR to SCA compliance to allow the use of JTRS JPO-provided waveforms. The DMR may be reconfigured completely via on-site or remote programming over a dedicated LAN or WAN. The four full-duplex programmable RF channels with coverage from 2.0 MHz to 2.0 GHz require no change in hardware to change waveforms or security.

The system is controlled, either locally or across the network, by a Windows-based HMI 23.JTRS (Joint Tactical Radio System)A set of current radio procurements for fully SDRs. These radio systems are characterized by SCA compliance that specifies an operating environment that promotes waveform portability. The JTRS JPO is procuring more than 9 increment one waveforms and more than 16 increment two waveforms that will ultimately be executable on JTRS radio sets. System packaging ranges from embeddable single-channel form factors to vehicle-mounted multichannel systems.

JTRS radios are the current state-of-the-art technology and have the highest level of software sophistication ever embedded into a radio 24.Other products related to SDR include GNURadio and the Vanu Anywave Base Station. GNURadio is a free software toolkit that is available on the Internet. It allows anyone to build a narrowband SDR. Using a Linux-based computer, an RF front end, and an analog-to-digital converter (ADC), one can build a software-defined receiver. By adding a digital-to-analog converter (DAC) and possibly a power amplifier, one can build a software-defined transmitter 25.The Vanu Anywave Base Station is a software-defined system that uses commercial off-the-shelf (COTS) hardware and proprietary software to build a wireless cellular infrastructure. The goal is simultaneous support for multiple standards, reduced operating expenses, scalability, and future proofing (cost-effective migration) 26. The adoption of RF transceivers with CR and software-defined radio (SDR)— frequency and modulation format agile—capabilities will lead to the adoption of such devices in industrial wireless sensors.

Wireless sensor hardware with optimal congestion management algorithms will coordinate their operation with gateway, access point, and router devices in network architectures that more efficiently utilize the available frequencies and times for transmission. The network designs associated with CR/SDR will interact with expansions of network management and intrusion detection systems that will include RF congestion management capabilities. The possible situation is outlined in Figure 11.15, where separate congestion management systems for geographically adjacent networks are coordinated through a shared suite of database systems. Such a situation could also alleviate the all-too-common occurrence of wireless sensors and systems deployed at adjacent industrial sites causing interference and suboptimal performance within the wireless sensor networks. Wyglinski, in, 2010 18.1 INTRODUCTIONA cognitive radio (CR) is a software- defined radio that is also capable of sensing its environment, track changes, and reacts upon its findings.

A CR is an autonomous unit in a communications environment that frequently exchanges information with the networks it is able to access as well as with other CRs. From our point of view, a CR is a refined SDR 650.

Presently, GNU Radio is widely used to implement cognitive radio designs, enabling both experimentation and research. Therefore, we focus mostly on GNU Radio in this chapter. 18.1.1 Introduction to GNU RadioAn SDR system is a radio communication system where components that have typically been implemented in hardware (e.g., mixers, filters, amplifiers, modulators/demodulators, detectors) are instead implemented using software on a personal computer or other embedded computing devices 651.

As a result, it transforms radio hardware problems into software problems. The fundamental characteristic of software radio is that software defines the transmitted waveforms and software demodulates the received waveforms. This is in contrast to most radios, in which the processing is done with either analog circuitry or analog circuitry combined with digital chips.Software radio is a revolution in radio design due to its ability to create radios that change on-the-fly, creating new choices for users. In theory, software radios can theoretically perform the same tasks as traditional radio systems. However, software radio systems also possess a substantial amount of flexibility, which provides the users and even the radio designers the options to create and employ advanced features deemed difficult by conventional radio systems. Controlling a computer, with necessary hardware supports, to play with radios should be easier, interesting, and attractive.GNU Radio is a free software toolkit for learning about, building, and deploying software radios 652.

GNU Radio provides a library of signal processing blocks and the connection to tie them all together. It is open source, which provides complete source code such that everyone can see how the system is built. To use GNU Radio, the communications systems engineer should be familiar with the following: First, some degree of competence with objected-oriented programming (OOP) is necessary, since GNU Radio employs both Python and C programming languages. Second, familiarity with the Linux operating system is required, since GNU Radio is particularly well-suited for this operating system.

Finally, expertise in wireless communication systems, digital signal processing, basic hardware, and circuit design are important. All of these will help you understand how GNU Radio works and implement your own system.

18.1.2 The Software. GNU Radio software architecture.This structure has some similarity with the OSI seven-layer data network model. The lower layer provides service to the higher layer, while the higher layer does not care about the implementation details carried on in lower layers, except for necessary interfaces and function calls. In GNU Radio, this layer transparency exists in a similar way. From the Python point of view, what it does is just selecting necessary signal sources, sinks, and processing blocks; setting correct parameters; then connecting them together to form a complete application.

In fact, all these sources, sinks, and blocks are implemented as classes in C. The parameter setting, connecting operations correspond to some sophisticated functions or class methods in C. However, Python cannot see how C is working.

A piece of lengthy, complicated, and powerful C code is nothing but an interface to Python.As a result, no matter how complicated the application is, the Python code is almost always short and neat. The real heavy load is thrown to C. One rule of thumb should be kept in mind: For any application, what we need to do at the Python level is to draw a diagram showing the signal flow from the source to the sink, sometimes with the support of graphical user interfaces ( GUIs).Knowledge of Python is crucial in learning GNU Radio. Python is a powerful and flexible programming language.

However, if one has a sufficient C/C background, it is not that difficult to learn. Considering that Python has some special characteristics when applied to GNU Radio and some of its useful features may not be necessary in GNU Radio, in Section 18.2 we talk more about combining the Python programming techniques and software radio concepts. 18.1.3 The HardwareThe universal software radio peripheral is designed to allow general-purpose computers to function as high-bandwidth software radios. In essence, it serves as a digital baseband and IF section of a radio communication system.The basic design philosophy behind the USRP has been to do all the waveform-specific processing, like modulation and demodulation, on the host CPU. All the high-speed general-purpose operations, like digital up- and down-conversion and decimation and interpolation, are done on the field-programmable gate array (FPGA). Wyglinski, in, 2010 7.1 INTRODUCTIONCognitive radios take advantage of the reconfigurable attributes of a conventional software-defined radio (SDR) by using an “intelligent” control method to automatically adapt operating parameters based on learning from previous events and current inputs to the system.

For cognitive radios to properly reconfigure, adapt, and optimize the system, several key parameters of the system must be identified. System parameters such as the transmission controls and environment measurements that are used to optimize the system must be identified. An optimization method, or “intelligent” control method, must be selected that can be run practically in real time to meet quality-of-service (QoS) requirements. The definition of these transmission parameters, environment parameters, and optimization techniques is at the core of the current cognitive radio research.

The momentum of research efforts, due in part to the current spectrum scarcity problem, as well as a Department of Defense initiative 234 to develop a flexible software radio approach for military communications, has yielded numerous initiatives and programs by researchers in academia 235 and industry 236. The resulting plethora of cognitive radio solutions range from cognitive radio components and radio network test beds 235 to complete radio systems 237.In this chapter we look at the commonly used wireless communication parameters that can be used by cognitive radios to optimize the performance of the system. We explore different objectives of communication to identify common cognitive radio goals that must be related to the parameters. These relationships give the cognitive engine the information needed to adapt the radio parameters to optimize the communication objectives.

We introduce several methods of optimizing wireless communication through the cognitive adaptation engine. We focus the discussion on the most commonly used techniques, including a heuristic-based method that uses genetic algorithms, an expert system technique that uses a rule-based approach, a case-based reasoning system that makes decisions based on past experiences, and hybrid techniques that use multiple combinations of these approaches.

IntroductionSoftware-defined radio (SDR) is a radio communication system where components that have been typically implemented in hardware (e.g. Please do not send e-mail to the development team unless absolutely necessary. The fount of all knowledge is the forum, several thousand happy members of this group are ready to help you.I prefer not to answer questions one to one, rather the user group as a whole as this is a much more efficient use of developer resources and encouages debate.AOL Note: I run my own e-mail server - Mail Enable on Windows Server 2016. AOL and some other ISPs block e-mails from IP addresses which are registered as being residential.

As a result my replies to AOL addresses are blocked, I am not prepared to fill in AOL's forms to possibly convince them to accept my e-mail server.